Why does the machine have to be on long enough to totally remove the emulsion- how about a limited blast to shake up or distort the silver image during development- could produce some innnerestin effects, methinks...

The cleaning effect of an ultrasonic cleaner is based on periodical contraction and expansion of the cleaning fluid. This causes so-called Kavitation Bubbles, tiny underpressure bubbles, that implode when they hit the cleaning targets. This impolsion mechanically removes more or less loose appendages. This happens sporadic. You have no real control over this process. Even a short burst or a burst at lower energy might locally affect the emulsion. Ultrasonic cleaning is a "stochastic" process. Increased duration only reduces the probability that there is still something left that could be removed...